Low-molecular-weight heparin (LMWH) is commonly used for preventing or treating venous thromboembolic disease (VTE) during pregnancy. The physiological changes in maternal metabolism have led to discussions on optimal LMWH dosing strategy and possible need for monitoring. The aim of this systematic review is to summarize and discuss whether LMWH dose adjustment according to anti-Xa provides superior effectiveness and safety compared with weight adjusted or fixed dosed LMWH in pregnant women. A systematic literature search was performed in PubMed, Embase, and Scopus on September 26, 2020. The study is reported according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Effectiveness was defined as episodes of thrombosis and safety as bleeding episodes. In total, 33 studies were included: 4 randomized controlled studies and 29 cohort studies. Prophylactic dosing strategies employing weight dosed, fixed dosed, or anti-Xa adjusted LMWH dosing performed equal in effectiveness and safety. In pregnant women with VTE or high thromboembolic risk, therapeutic weight-adjusted LMWH and weight plus anti-Xa-adjusted LMWH provided equal results in terms of effectiveness and safety. Pregnant women with mechanical heart valves (MHVs) received therapeutic anti-Xa-adjusted LMWH with four out of seven studies presenting mean peak anti-Xa within target ranges. Still, pregnant women with MHV experienced both thrombosis and bleeding with anti-Xa in target. Based on the results of this systematic review, current evidence does not support the need for anti-Xa monitoring when using LMWH as thromboprophylaxis or treatment during pregnancy. Nonetheless, the need for anti-Xa monitoring in pregnant women with MHV may need further scrutiny.
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